Embodiments according to the invention are related to a signal converter for generating switch drive signals for a multi-level converter, a drive circuit for generating switch drive signals for a multi-level converter, a pulse-width-modulation signal generator for generating two pulse-width-modulation signals and a polarity signal and to a multi-level converter. Some further embodiments according to the invention are related to a method for driving at least four switches in a switch circuit of a multi-level converter and to a method for generating two pulse-width-modulation signals and a polarity signal. Some other embodiments according to the invention are related to computer programs. Some embodiments according to the invention are related to a 3-level hybrid drive system.
In many technical applications, it is desirable to convert supply voltages between different voltage levels and/or frequencies. For example, in some applications it is desirable to generate a supply voltage of a predetermined amplitude and/or predetermined waveform from one or more supply potentials. One possibility for generating a desired voltage or current signal on the basis of three different potentials is to use a 3-level pulse-width-modulation (PWM). 3-level pulse-width-modulation is for example used for railway driving apparatuses and for medium high voltage converters.
Since approximately one year, the 3-level circuit concept is increasingly getting relevant for uninterruptable power supplies (also designated as “UPS” or “USV”), for example in a power range of about 7.5 kVA, i.e. for the mass market. The 3-level solution, which is more complex with respect to the circuitry when compared to the previous standard topology of this application, the 2-level converter, has decisive advantages with respect to the overall efficiency and—except for the increased drive effort of a conventional 3-level solution—with respect to the total costs of such a uninterruptable power supply system.
In the following, some characteristics of conventional systems for generating a three-phase signal will be discussed. However, there are naturally also some one-phase systems or two-phase systems.
While 2-level topologies (for example for generating a 3-phase signal) get by with 6 generated switch signals, some 3-level topologies (e.g. for a 3-phase signal) need twelve drive signals for the power elements. Accordingly, it is more complicated and complex to generate these control signals (or drive signals, or switch signals).
In 3-level medium high voltage converters and railway converters, professional digital signal processors (“DSP”) or “field programmable gate arrays” (“FPGA”) are used in order to generate the twelve control signals (or drive signals). In contrast, for 2-level topologies, there are some very inexpensive standard microprocessors (or microcontrollers) available, even in the low cost domain, comprising the pulse-width-modulation unit with dead time generation for six switch elements already integrated.
In view of the above discussion, there is a need for a cost-efficient concept for generating the drive signals for a multi-level converter.
This need is satisfied by some embodiments according to the invention.